I have read a few posts that say ICMP is "probably" low priority in the OS, which explains things like the thinkbroadband BQM graphs showing high latency, but is this a 'definite'? I too am seeing very high latency per the BQM on my 500Mb/s BT FTTP link and am trying to get to the bottom of it. The think broadband forum is very helpful, but they aren't Draytek experts and if ICMP is indeed deprioritised then that's probably my answer.

As a test I used App QoS to assign ICMP to Class 1 with nothing else configured in QoS and didn't see any improvement.

Does anyone have any insights?

I've always thought this an old-wives's tale

(It came up a lot on Virgin Media's forums, when the VM Hub3 was suffering its latency woes - along with statements like "It can never be fixed. it's a chipset problem". (The latter statement being demonstrably incorrect!))

In any case, 'low priority' would only have any bearing, if there was lots of other traffic, to take priority. In other words, you would only see the effect if the line was otherwise busy - ICMP wouldn't ordinarily be delayed for no reason. This logic applies to "QOS" too.

That's my twopenneth - but I don't have access to Draytek's source code

Whatever it is, I would be interested in understanding why I am seeing the figures on the BQM here - https://www.thinkbroadband.com/broadband/monitoring/quality/share/6774a13781f4bc5d51d61800bbaf1bb62e841d4c-20-11-2021

...the ones to the left of the red bar from ca. 10.30-11.30. To the right, post 11.30, are the results when connected the BT FTTP line to an EdgerouterX.

Surely there's an explanation for the results I am seeing when using the 2926? I have tried a full reset and reload via the .rst firmware, tried turning the firewall off, changing the MTU to 1500 from 1492, dancing around the router chanting incantations and swearing at it.

....any thoughts or insights would be greatly appreciated!

There's a guide here. Have you read it? https://www.thinkbroadband.com/faq/broadband-quality-monitor

I actually read it yesterday but I don't think it addresses what I am seeing. I am just wondering why the BT link shows far more latency when connected to my 2926 than to a ERX or even my laptop via PPPOE.

nieldm wrote:
....any thoughts or insights would be greatly appreciated!

Are you perhaps triggering some Denial-of-Service Defence ?

It could be the default values are too low for the speed of the line?